Process for manufacturing highly emissive cathodes



B. LOEWE July 4, 1933.

PROCESS FOR MANUFACTURING HIGHLY EMISSIVE CATHODES Filed Feb. 26, 1929 Patented July 4, 1933 UNITED STATES PATENT OFFICE BERNHARD LOEWE, O1 BERLIN, GERHAN'Y Application filed February 26, 1929, Serial No. 342,930, and in Germany February 28, 1928.

The invention .relates to a process for manufacturing a suitable source of emission for audions such as amplifier or detector valves.

5 According to the invention the cathode is coated with a highly emitting metallic material such as barium, strontium, calcium or compounds of the same, the coating taking place, if necessary, after a suitable preparatory treatment of the surface of the cathode.

It is the essence of the invention that at least two substances are made to react (binary chemical reaction) in such a manner that the desired highly emitting substance, for im stance barium, is liberated as a metal and deposited on the cathode. The process may be described by way of example.

A powdery compound of barium oxide and silicon is introduced into the valve to be evacuated. Appropriately the compound is compressed to tablets, if necessary adding agglutinants or substances retarding the reaction, and introduced into the valve in such a manner that a heating of the compound may take place. It then appears that heating the tablet in the vacuum causes a reaction so that silicon oxide is formed on the onehand and metallic barium on the other. Preferably a vacuum of 10- to 10" mm is used and the reaction allowed to take place when the tablet is brightly glowing. The metallic bari um is dispersed in the vacuum in form of a metal vapour and, precipitates particularly on the surface of the cathode.

The process may be further developed in that the reactive components themselves may either be brought on to the surface of the cathode or directly form the cathode. If, in this case, the reactive surface of the cathode is heated or exposed to an electric discharge, the reaction in the respect above indicated takes place in such a manner that perpetually small quantities of metallic barium are formed.

But according to the invention only in the case if the emitting metal is to be the product of a permanent reaction in the manner described above, the reactive components are brought onto the surface of the cathode itself,

' whilst the chief object of the invention, consists in arranging the reactive components not on the cathode itself, but at a place of the discharge device particularly provided for thls urpose and in heating them separately. n this case it is of great advantage that only the pure metal is precipitated to the cathode itself and that the secondary products of reaction remain there where the reaction components are arranged.

It is an essential feature of the invention that in contradistinction to all processes. hitherto known the highly emitting substance coating the surface of the cathode is the product of an at least a binary chemical reaction between reactive components arranged at a place outside the cathode.

Furthermore it is essential for the invention that the development of .the highly emitting substance takes place while the valve is connected with the pump. Thus the electron discharge device according to my invention is simply manufactured.

In like manner metallic sodium, potassium and other suitable metals may be produced inside the valve itself by bina reaction. The process may also be repeate y applied by several different metals being produced successively or simultaneously by the reaction of suitable compounds.

Instead of silicon ferro-silicon, aluminium, magnesium or the like may be used. The separate dispersion of a metal, e. g. magnesium, as a'getter may be avoided since the liberated metal vapour has a clean-up effect.

My invention may be best understood with reference to the accompanying drawing.

Figs. 1 and 2 illustrate two forms of construction of the inside of audions manufactured by the process according to the invention.

Fig. 1 shows the triode system supported by a valve pedestal 1 and consisting of cathode 2, grid 3 and anode 4 (out half 'through). Inside the anode a tablet 5 has been arranged which consists of the compound which according to the invention shall be used for the reaction.

In Fig. 2 a cup-shaped metal pedestal 6 is arranged at the side of the triode system. In that metal pedestal the substance to be used and heating for the reaction is arranged at the bottom so that, if the metal cup is heated, for instance b electron bombardment (if the cup is joined to a suitable potential) or by high frequency currents, the reaction may e started or maintained.

1. A method of producing a highly emissive cathode for electron emission purposes, comprising the steps of arranging a refractory filament in a vacuum, placing adjacent thereto a mixture of an earth alkaline oxide and a reducing agent, the heat of reaction of this mixture being small when reacting, and heating said mixture to cause the earth alkaline metal to be liberated and vaporized onto the filament to form a thin earth alkaline metal layer on said filament.

2. A method of producing a highly emissive cathode for electron emission purposes, comprising the steps of arranging a refractory filament in a vacuum, placing adjacent thereto a mixture of a barium oxide and a reducing agent, the heat of reaction of this mixture being small when reacting and heating said mixture to cause the metallic barium to be liberated and vaporized onto the filament to form a thin metallic barium layer on said filament. v

3. A method of producing a highly emissive cathode for electron emission purposes, comprising the steps of arranging a refractory filament in a vacuum, placing adjacent thereto a mixture of barium oxide and silicon said mixture to cause metallic barium to e liberated and vaporized onto the filament to form a thin metallic barium layer on said filament.

4. A method of producing a highly emissive cathode for electron emission purposes, comprising the steps of arranging a refractory filament in a vacuum, placing adjacent I thereto a mixture of barium oxide and ferrosilicon and heating said mixture to cause metallic barium to be liberated and vaporized onto the filament to form a thin metallic barium layer on said filament.

5. A method of producing a highly emissive cathode for electron emission purposes, comprising the steps of arranging a refractory filament in a vacuum, placing adjacent thereto a mixture of barium oxide and aluminium, and heating said mixture to cause metallic barium to be liberated and vaporized onto the filament to form a thin metallic barium layer on said filament.

6. A method of producing a highly emissive cathode for electron emission purposes, comprising the steps of arranging a refractory filament in a vessel, placing adjacent thereto a mixture of an earth alkaline oxide and a reducing agent, the heat of reaction of this mixture being small when reacting, evacuating said vessel to produce a vacuum of less than 10" mm, and heating said mixture during the evacuating process to cause the earth alkaline metal to be liberated and vaporized onto said refractory, filament to form a thin metallic layer coating said filament, and sealing said vessel.

In testimony whereof I have afiixed my signature.

BERNHARD LOEWE. 

